Although the development of preventative vaccines has significantly reduced the mortality rate of viral infections, the use of such vaccines against viruses that cause persistent infections (e.g., hepatitis C virus) has been met with limited success. In contrast to viruses that cause acute and self-limited infections, the immune response that is mounted against persistent infection-causing microbes is often transient and insufficient to clear the infection. As a result, the infectious microbe remains within the infected subject for extended periods of time, without necessarily causing constant host damage.
A major impediment in the eradication of persistent infection-causing microbes is the ability of such microbes to evade the immune system of the host organism. For example, certain viruses and parasites down-regulate the expression of host molecules necessary for efficient T cell recognition of infected cells. Persistent infections also cause the functional impairment of antigen specific CD8+ T cells, which are vital to the control and eradication of viral infections. Although the combination of therapeutic vaccines with cytokine adjuvants has been encouraging, the resulting immune responses have not successfully eradicated the pathogen.
Thus, better methods are needed to treat, prevent, or alleviate persistent infections.